As this kind of marker lamp, a configuration including a first light source, a second light source, and a light guide has been known (see, e.g., Japanese Patent No. 4979565). The light emitted from the first light source and the light emitted from the second light source are incident on the light guide. The light incident on the light guide is repeatedly reflected within the light guide and emitted as an illumination light from a predetermined emitting surface. The illumination light illuminates a predetermined illumination range based on a predetermined illumination standard. The illumination light is visually recognized by a pedestrian or a driver of a front vehicle, so that the presence of the vehicle on which the marker lamp is mounted is recognized.
The marker lamp having the configuration as described above cannot satisfy the predetermined illumination standard when turning-on of any one of the first light source and the second source is disabled for a certain reason. In such a case, a controller including a driver circuit of the first light source and the second light source is generally configured to prohibit turning-on of the other one of the first light source and the second light source. The marker lamp in which the illumination light is unable to be emitted will be repaired or replaced.